Dept. of Mech & Mfg. Engg. 1 Instructions GENERAL: Enter the room In Time. Switch off your mobile phones. Dont use Lap Tops during my lecture. Maintain.

Dept. of Mech & Mfg. Engg. 1

Instructions

GENERAL:• Enter the room In Time.• Switch off your mobile phones.• Don’t use Lap Tops during my lecture.• Maintain Discipline inside the class.• Maintain one Separate Note book.• Note down Sketches, important points and

definitions.


InstructionsMark distribution:

Test = 40 marks

Assignment / surprise test = 10 marks

End Sem Exam = 50 marks

Test: 40 marks• There will be 3 Tests. • Each test is of 20 marks (10 each from 2 parts)• Out of 3 tests, best 2 are considered.

Assignment / surprise test:• There will be 3 assignments / surprise tests.• Each assignment / surprise test is of 10 marks.• To award 10 marks, all are considered.


Reference books

1. Mechanical Engineering Science: K.R. Gopalakrishna, Subhas Publications

2. Elements of Mechanical Engineering: Roy & Choudhury, Laxmi Publications Pvt. Ltd

3. Mechanical Engineering Science: B.K. Mishra, Kumar & Kumar Publishers Pvt. Ltd

4. Mechanical Engineering Science: R.K Rajput, Laxmi Publications Pvt. Ltd.


MES

Part A Part B

1. Properties of steam2. Steam boilers3. Steam turbines4. Refrigeration5. I C engines6. Lubrication

1. Transmission of power2. Machine tools 3. Casting 4. Forging5. Welding


Chapter 1: PROPERTIES OF STEAM

• Define steam:

• Vapour form of water is called STEAM.

• Water in solid phase: We call it as ICE• Water in liquid phase: We call it as WATER • Water in gaseous phase: We call it as STEAM.


Application of steam

Food processing industry.

Cooking: hotels, restaurants etc.

Used as a working fluid in steam engines and steam turbines.

Used in industries for process heating.

Petrochemical industry.

Washing/drying/sterilizing in hospitals.

Health clinic / gym.


Formation of steam experiment

• Consider 1 kg of water at 0oC taken in a cylinder fitted with a freely moving frictionless piston as shown in fig.

W

Cylinder

1 kg water at 0oC

Pressure ‘P”


The initial condition of water at 0oC is represented by the point A on the

temperature-enthalpy graph

A

Temperature

Enthalpy (h)

Temperature (T)oC


A

Temperature

Enthalpy (h)

Temperature (T)oC

TSat B

hf

Sensible heat

hfg

Latent heat

TSup

AOS

C

D

DOS

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

A B C D


Definitions • Sensible heat (hf) : It is defined as the

amount of heat required to raise the temperature of 1 kg of water from 00C to the saturation temperature Tsat °C at a given constant pressure.

• Saturation temperature( Tsat): It is defined as the temperature at which the water begins to boil at the stated pressure


• Latent heat of evaporation (hfg): It is defined as the amount of heat required to evaporate 1 kg of water at saturation temperature to 1 kg of dry steam at the same saturation temperature at given constant pressure

• The temperature of the steam above the saturation temperature at a given pressure is called superheated temperature (Tsup)


• Amount of superheat (AOS) or enthalpy of superheat: It is defined as the amount of heat required to increase the temperature of dry steam from its saturation temperature to any desired higher temperature at the given constant pressure.

• Degree of superheat (DOS): It is the difference between the superheated temperature and the saturation temperature.


Different states of steam.

• The steam as it is being generated can exist in three different states,

• 1. Wet steam• 2. Dry saturated steam• 3. Superheated steam.


Wet Steam:

• A wet steam is defined as a two-phase mixture of finely divided water particles and dry steam in thermal equilibrium at the saturation temperature corresponding to a given pressure.


• The quality of the wet steam is specified by the dryness fraction which indicates the amount of dry steam present in the given quantity of wet steam and is denoted as x.

• The dryness fraction of a steam is defined as the ratio of mass of the actual dry steam present in a known quantity of wet steam to the total mass of the wet steam.

Steam Wet of Mass Total

Steamin Wet present SteamDry of Mass x fraction, Dryness


• Let mg = Mass of dry steam present in the sample quantity of wet steam

• mf = Mass of suspended water molecules in the sample quantity of wet steam

• x = mf+ mg

• mg

• The dryness fraction of the wet steam will be less than 1.


Dry Saturated Steam:

• A saturated steam at the saturation temperature corresponding to a given pressure and having no water molecules entrained in it.


Superheated Steam:

• A superheated steam is defined as the steam which is heated to temperature higher than its saturated temperature at the given pressure.


• Advantages of Superheated Steam:• At a given pressure, the superheated steam possess

more heat energy compared to dry saturated steam or wet steam at the same pressure, hence its capacity to do the work will be higher.

• When superheating is done by the exhausting combustion gases in a boiler, there will be a saving of the energy of combustion which improves the thermal efficiency of the boiler.

• While expanding in a steam turbine it reduces and in extreme cases prevents the condensation, thus giving better economy.

• Disadvantages of Superheated Steam:– The high superheated temperatures poses problems

in the lubrication.– Higher depreciation and initial cost.


Enthalpy equations for different states of

steam a) Enthalpy of Dry saturated Steam:

hg = hf +hfg kJ/kg

A

B C

SensibleHeat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of Superheat

Degree of Superheat

Ts

hf

D

Temperature


b) Enthalpy of Wet Steam:

h = hf +x hfg kJ/kg

A

B C

SensibleHeat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of Superheat

Degree of Superheat

Ts

hf

D

Temperature


c) Enthalpy of Superheated Steam: hsup = hf +hfg + Csup(Tsup - Tsat) kJ/kg

A

B C

SensibleHeat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of Superheat

Degree of Superheat

Ts

hf

D

Temperature


d) Degree of superheat (DOS): DOS = (Tsup - Tsat)

A

B C

SensibleHeat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of Superheat

Degree of Superheat

Ts

hf

D

Temperature


e) Amount of superheat (AOS): AOS = Csup (Tsup - Tsat)

A

B C

SensibleHeat

Latent Heat

hfg

Tsup

Temperature

Enthalpy

Amount of Superheat

Degree of Superheat

Ts

hf

D

Temperature

Dept. of Mech & Mfg. Engg. 1 Instructions GENERAL: Enter the room In Time. Switch off your mobile phones. Dont use Lap Tops during my lecture. Maintain.

Documents

temperature of dry steam

superheated steam

steam engines

steam turbines

steam boilers

dry saturated steam

given quantity of wet

properties of steam